When It comes to heroic healing dungeon healing there is one preaty big point that the above posts tend to miss or gloss over, for lack of a better analogy, shaman go forth and shaman. Simply put, shaman are the most "offensive" healers in wow, you should use all tools you have, many often overlook the fact the best heals are the ones you never have to cast.
Interrupts:
Wind Shear. It is amazing use it a lot. Interrupting a range to bring it to the tank cuts down damage significantly, a tank going to round up a loose mob often puts his back to the group, this is very bad. Also when you have little damage coming in watch a burn target and help on interrupts.
Grounding Totem: It gets no love these days but if Wind shear is on CD grounding can eat the bad spell, saving a lot of damage.
Hex/Bind Elements: don't forget that these spells interrupt casts as well, even if the CC will break again in a few moments or instantly, it still stops the cast.
Crowd Control:
Now with Hex and Bind Elements we are one of the best CC classes in the game. While healing you may not be the main CC'er look what you can do and who is doing what kind of other CC's and what the cast times cool downs and durations are. When there is a lot going on and the dps is "trying" to get of the fire they may not notice that a CC broke, rather than let Whirlwindy the Big Axe Ogre go have a mage sandwich, Hex it. If you see a CC about to break and no "re-sheep" is incoming Hex/bind it.
Dps:
Yeah that's right dps, some mobs out there go BOOM after a set amount of time or lock people in bubble shields, in cases where no one needs instant healing help dps. Think about it whats worse on your mana, using a Healing surge to top someone off quick and helping the dps beat a damage timer, or using healing wave pre-blast to top someone up only then have an aoe rock the party a few moments latter. Even a simple set it and forget it flame shock can and does help.
Purge:
While used very little, when a mob has a buff that can be purged 9/10 times you will be far better off purging than casting anything else. Purge when it can be used is a huge damage reduction.
This list does go on, Frost Shock, Earth Shock, ect.
One final thought, in many forum threads and even in this one, you find people saying "it's the dps's job to reduce incomming damage" well it's yours as well. Be a team player help the dps and the tank do their jobs, and yours will be much easier.

